Fluid injection element for a furnace or a burner of a furnace and method for operating a furnace

ABSTRACT

A fluid injection element is disclosed, especially for a furnace or a burner of a furnace, having a pipe and a shroud element, such that the shroud element circumferentially surrounds an axial section of the pipe extending from an axial end of the pipe, such that at least one cavity is provided at the shroud element, and the at least one cavity is in fluid communication with an interior of the pipe and the at least one cavity extends to an opening at an axial end of the shroud element.

BACKGROUND OF THE INVENTION

The present invention relates to a fluid injection element, especially for a furnace or a burner of a furnace, to a furnace and to a method for operating a furnace.

Flameless and semi flameless burner technologies can be used in furnaces to perform combustion of a fuel, e.g. natural gas, methane and/or propane, and an oxidant, usually air and/or oxygen. An off-gas or combustion gas is produced in the course of combusting, for example comprising carbon dioxide CO₂ and vapour H₂O.

For example, these kinds of flameless or semi flameless burners can be provided as so called oxy-fuel burners, which combust the fuel with high purity oxygen as an oxidant instead of atmospheric air. In so called low temperature oxy-fuel burners (LTOF) the combustion can occur under a diluted oxygen concentration by mixing furnace gases into the combustion zone. In these kinds of burners, the fuel and the oxidant are usually provided separately via individual supply mechanisms. The oxidant can particularly be provided via a particular fluid injection element which can e.g. be provided as an oxidant lance.

These flameless and semi flameless burner technologies all rely on the very high velocity oxidant or oxygen jets to generate the flameless effect. The oxygen outlet velocity is typically the speed of sound in oxygen, around 305 m/s. Velocities from about 100 m/s upwards can also be used. The high velocity jets create a very strong recirculation within the furnace gas space, resulting in a reduced NOx generation by reducing peak temperatures within the flame and in a very homogeneous heating of the furnace. Such burner technologies have proven very efficient and useful especially in essentially clean dust free furnace atmospheres.

Burners of that kind can e.g. be used in melting furnaces for the melting of metallic materials, for example in lead recycling furnaces or in aluminium melting furnaces. Furnaces of that kind can e.g. be provided as rotary furnaces, wherein a corresponding burner can be arranged in a furnace door through which the material to be melted can be introduced into the furnace.

SUMMARY OF THE INVENTION

According to the present invention a fluid injection element, especially for a furnace or a burner of a furnace, a furnace and a method for operating a furnace according to the independent claims are provided. Preferred embodiments and advantages of a method and a furnace according to the invention are subject of the dependent claims and of the following description.

The fluid injection element comprises a pipe and a shroud element, wherein the shroud element circumferentially surrounds an axial section of the pipe extending from an axial end of the pipe. Thus, the shroud element is particularly arranged at an end portion of the pipe. It is, however, also possible that the shroud element surrounds the entire pipe. The shroud element can e.g. be firmly bonded to the pipe, especially by means of a welding joint.

According to the present invention, at least one cavity is provided at the shroud element, wherein the at least one cavity is in fluid communication with an interior of the pipe and wherein the at least one cavity extends to an opening at an axial end of the shroud element.

The pipe is particularly formed such that a fluid can be conducted through the interior of the pipe and can be for ejected throughout the axial end of the pipe. Thus, a first jet or stream of the corresponding fluid can particularly be created.

With the cavity being in fluid communication with the interior of the pipe, a certain amount of the fluid can pass from the interior of the pipe into the cavity and can be ejected throughout the opening of the axial end of the shroud element. Thus, a second jet or stream of the corresponding fluid additionally to the first jet can be created.

In particular, by means of the specific dimensions of the cavity and the specific way in which the fluid communication is established, the specific amount of fluid which passes through the cavity and is ejected in the form of the second jet can be adjusted. Furthermore, the speed with which the corresponding amounts of fluid are ejected can especially be adjusted. The first jet particularly has a comparatively high velocity whereas the second jet particularly has a lower velocity than the first jet.

The creation of this second jet yields distinct advantages when the fluid injection element is used in a furnace with a dirty or dusty atmosphere, particularly for providing an oxidant to a burner. In a common furnace comprising a burner with common oxidant lances without the creation of a second jet of that kind there is the danger that accretions can build around the oxidant lances. For example in furnaces with a dirty or dusty environment or an environment with entrained liquid droplets, these particles or droplets are recirculated, and, due to their higher momentum, tend to be deposited on the refractory wall surrounding the outlets of these common oxidant lances. Such deposits are also sometimes referred to as accretions. These either block the outlets or disturb the gas jets and reduce its recirculating efficiency. These accretions can build over short periods of time, even within one charge. This causes high maintenance and/or reduces the typically benefits of NOx reduction and homogeneous heating. The deposits could also deflect the high speed jet towards the furnace refractory wall causing severe damage. In the worst case, combustion system safety can no longer be guaranteed.

When a fluid injection element according to the present invention is used in a furnace for providing an oxidant to a burner, the creation of accretions of that kind can particularly be prevented or at least significantly reduced. By means of the fluid injection element a first oxidant jet can be created when the oxidant is ejected throughout the axial end of the pipe and a second oxidant jet can be created when the oxidant is ejected from the opening at the axial end of the shroud element. This second oxidant jet is particularly sucked into the first oxidant jet at a position relatively close to the axial ends of the pipe and the shroud element. Therefore, in this zone, in which the second oxidant jet is sucked into the first oxidant jet, dust or dirt particles or droplets are not sucked into the first oxidant jet. The recirculation zone, in which these kinds of dust, dirt, particles or droplets are recirculated by the oxidant jets, is therefore moved further inside the furnace away from the axial ends of the pipe and the shroud element. Thus, these kinds of particles are prevented from depositing on or near or around the tip of the fluid injection element. Therefore, by means of the present fluid injection element maintenance intervals of furnaces can be increased, thereby reducing costs and effort to operate the furnace and to keep the furnace in optimum working conditions.

The present invention further relates to a corresponding furnace, especially a melting furnace, for example a lead recycling furnaces or an aluminium melting furnaces, which comprises a burner with a fuel supply and an oxidant supply. Further, the furnace comprises at least one fluid injection element according to the present invention for providing an oxidant to the burner.

Further, the present invention relates to a method for operating a furnace, especially a melting furnace, for example a lead recycling furnaces or an aluminium melting furnaces. According to the present method fuel is provided to a burner of the furnace. An oxidant is provided to the burner via at least one a fluid injection element according to the present invention such that a first amount of the oxidant is provided with a first velocity and a second amount of the oxidant is provided with a second velocity smaller than the first velocity. Particularly, this first velocity is a sonic or supersonic velocity. The second velocity is particularly a subsonic velocity.

For example, natural gas, methane or propane e.g. with the addition of coke in the charge mix as a reducing agent can be provided as fuel. As oxidant air and/or oxygen are particularly provided.

Therefore, according to the present invention a fluid, particularly an oxidant for the burner of the furnace, conducted through the fluid injection element can be separated in two different streams or jets. A high velocity first oxidant jet particularly with sonic or supersonic velocity and a low velocity second oxidant jet particularly with subsonic velocity are created. By means of these two separated jets no or at least essentially no accretions are created at the tip of the injection element.

According to a preferred embodiment of the present invention, an opening in a wall of the pipe connects the interior of the pipe and the at least one cavity thereby establishing the fluid communication between the interior of the pipe and the at least one cavity. This wall of the pipe extends with a distance to the shroud element, the distance being constant or variable. Particularly, by the specific dimensions of this opening in the wall the specific amount of fluid passing through the cavity as well as the velocities of the first and second jets can be adjusted. In principle, the cavity can also be formed by a projection part of the shroud element itself, the projection part extending with a distance to the remaining shroud element and having an opening for connecting the cavity with the interior of the pipe.

According to a particularly preferred embodiment, the pipe has at least three different axial sections, wherein the diameter of the interior of the pipe is different in these three sections. In a first axial section of the pipe the diameter of the interior of the pipe advantageously has a first (constant or variable) value. In a second axial section of the pipe subsequent to the first section the diameter of the interior of the pipe preferably decreases from the first value to a second (constant or variable) value. In a third axial section of the pipe subsequent to the second section the diameter of the interior of the pipe advantageously has the second value. Preferably, this third section axially extends to the axial end of the pipe. Advantageously, the shroud circumferentially surrounds at least the second section and the third section. Particularly, these second and third section form a narrowing of the interior of the pipe and thus form a nozzle. Thus, the pressure of the fluid conducted through the interior of the pipe can particularly be increased by means of this nozzle and the fluid can be ejected throughout the end of the pipe preferably at sonic of supersonic velocities. The shroud element particularly surrounds this nozzle.

Advantageously, the opening in the wall of the pipe connecting the pipe and the at least one cavity is provided in the second section. Thus, by means of this opening in the second section the fluid communication between the cavity and the interior of the pipe is established and fluid can pass into the cavity in this second section.

Advantageously, one single cavity is provided at the shroud element which continuously extends in a circumferential direction inside the shroud element. Thus, this one cavity circumferentially surrounds the pipe or at least a corresponding section of the pipe. The corresponding opening of this cavity therefore circumferentially surrounds the axial end of the pipe. Thus, by means of this cavity one single second jet can be created which surrounds the first jet ejected from the axial end of the pipe, particularly in a “donut shape”.

Alternatively, several cavities are advantageously provided inside the shroud element distributed in predetermined circumferential distances to each other. Thus, also these several cavities circumferentially surround the pipe or at least a corresponding section of the pipe. These can be provided in equidistant circumferential distances to each other or also in individual different distances. Further, also the openings of these cavities circumferentially surround the axial end of the pipe. Thus, several second jets can be created which surround the first jet, particularly in a “donut shape”.

In an analogous manner, according to the present method the first amount of the oxidant is preferably provided as a first oxidant jet and the second amount of the oxidant is preferably provided as at least one second oxidant jet circumferentially surrounding the first oxidant jet. Thus, in particular, by means of the at least one cavity one or several second low velocity jets are created which surround the first higher velocity jet, particularly with the first jet in their centre.

Preferably, at least one bleed hole is provided in the shroud element extending from the at least one cavity to an outer end or radial end of the shroud element. Particularly, this at least one bleed hole extends in a radial direction or at least essentially in the radial direction and especially extends to an outer radial end of the shroud element. Particularly, this bleed hole is provided as a low pressure or low velocity bleed hole for pressure compensation.

Advantageously, an expansion of the at least one cavity in radial direction has different values or differently varying values in different subsequent axial sections of the at least one cavity. Therefore, the radial expansion of the cavity is partially not constant along an axial direction, but varies. Thereby, fluid dynamic of the second jet can particularly be influenced. Particularly, in each axial section the radial expansion varies in a specific way, i.e. either reduces or enlarges in a specific way along an axial direction. Especially, in subsequent axial sections the reducing/enlarging character of the cavity alternates, i.e. in one section the radial expansion reduces, in the subsequent axial section the radial enlarges and so on. Particularly, the cavity comprises three axial subsequent sections, wherein in a first axial section the expansion enlarges, in a subsequent second axial section the expansion reduces, and in a third subsequent axial section the expansion enlarges again. It is also possible that only two sections provided wherein in a first section the expansion enlarges and in a subsequent second section the expansion reduces.

Advantageously, the pipe is adapted to be connected with a fluid supply such that a first amount of a fluid is conducted through the interior of the pipe and ejected throughout the axial end of the pipe with a first velocity, preferably with a sonic or supersonic velocity, and such that a second amount of the fluid is conducted through the at least one cavity of the shroud element and ejected throughout the opening of the at least one cavity at the axial end of the shroud element with a second velocity smaller than the first velocity. In an analogous manner, according to the present method the first amount of the oxidant is advantageously provided via the interior of the pipe of the at least one fluid injection element and the second amount of the oxidant is advantageously provided via the at least one cavity of the shroud element of the at least one fluid injection element. Thus, the inside of the shroud element, which is usually not used for any purposes, can be used for creating the second jet.

Preferably, the first amount of the fluid, particularly the oxidant, is between 75% and 90%. The second amount of the fluid, particularly the oxidant, is advantageously between 10% and 25%.

Further advantages and developments of the invention are specified in the description and the associated drawings.

It goes without saying, that the features named above and still to be explained below can be used not only in the combination indicated respectively, but also in other combinations or in a stand-alone manner, without going beyond the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated schematically in the drawings on the basis of exemplary embodiments and will be described in detail in the following with reference to the drawings.

FIG. 1 is a schematic showing a melting furnace with a fluid injection element according to a preferred embodiment of the invention in a sectional side view.

FIG. 2a is a schematic showing a preferred embodiment of a fluid injection element according to the present invention in a sectional side view.

FIG. 2b is an enlarged view of the shroud element.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 schematically shows a melting furnace 100 according to a preferred embodiment of the invention in a sectional side view.

In the present example, the melting furnace 100 is a rotary furnace. However, the melting furnace 100 could also be of a different kind, for example a reverberatory furnace or the like.

The melting furnace 100 comprises a chamber 101 in which a metallic material 103 to be melted can be provided. For example, the melting furnace 100 can be provided to melt an aluminium material 103. The chamber 101 can be locked with a door 102.

An exhaust flue 104 for exhausting waste gas from the chamber 101 is provided such that an opening of the exhaust flue 104 is arranged in the door 102.

Further, a burner 105 is provided in the door 102. The burner 105 comprises a fuel injection element 110, which is fluidly connected with a fuel supply 111 such that a fuel, e.g. natural gas, methane or propane, can be provided to the burner 105. The burner 105 further comprises at least one oxidant injection element 120. Though only one oxidant injection element 120 is shown in FIG. 1 for reasons of clarity, the burner 105 can comprise several oxidant injection elements 120, preferably two or four oxidant injection elements 120. Each of these oxidant injection elements 120 is connected with an oxidant supply 121 and is arranged inside the door 102 for providing an oxidant to the burner 105, e.g. oxygen.

A control unit 140 is provided for operating the melting furnace 100. For this purpose, the control unit 140 is particularly adapted to perform a preferred embodiment of a method according to the invention.

According to this method, the oxidant, e.g. oxygen is provided is provided in the form of two different oxidant jets 130, 131. By means of each oxidant injection element 120 a first amount of the oxidant, e.g. 90% of the oxidant is provided in the first jet 130 with a sonic or supersonic velocity. A second amount of the oxidant, e.g. 10% is provided in the form of second jets 131 surrounding the first jet 130 with a velocity smaller than the velocity of the first jet 130.

For this purpose, each oxidant injection element 120 is provided as a fluid injection element according to a preferred embodiment of the present invention. A fluid injection element of that kind according to a preferred embodiment of the present invention is schematically shown in FIG. 2a and referred to as 200.

As shown in FIG. 2a , the fluid injection element 200 comprises a pipe 210 and a shroud element 220, which circumferentially surrounds an axial section of the pipe 210 extending from an axial end 211 of the pipe 210. The shroud element 220 can e.g. be made of 304 grade stainless steel or preferred 316 L stainless steel or Inconel 600.

FIG. 2b shows an enlarged view of the shroud element 220, when the fluid injection element 200 is arranged inside the door 102.

As can be seen in FIG. 2b , the shroud element 220 comprises cavities 221, which are in fluid communication with an interior 212 of the pipe 210 by means of openings 213 in a wall of the pipe 210. The cavities 221 extend from these openings to openings 222 at an axial end 223 of the shroud element 220.

By means of these cavities 221 in the shroud element, the first amount of e.g. 90% of the oxidant is conducted through the interior 212 of the pipe 210 and ejected throughout the axial end 211 of the pipe 210 in form of the first jet 130 with a first velocity, particularly a sonic or supersonic velocity.

Further, the second amount of e.g. 10% of the fluid is conducted through the cavities 221 of the shroud element 220 and ejected throughout the openings 222 of the cavities 221 at the axial end 223 of the shroud element 220 in the form of the second jet with a second velocity smaller than the first velocity.

Further, a bleed hole 224 can be provided extending in radial direction from the cavity 221 to an outer end or radial end of the shroud element 220. This bleed hole 224 can be provided as a low pressure or low velocity bleed hole such that oxidant 132 can be ejected for reasons of pressure compensation.

As can be seen in FIG. 2b , the pipe comprises three different axial sections. In a first axial section 231 of the pipe 210 the diameter of the interior 212 of the pipe has a first value. In a second axial section 232 subsequent to the first section 231 the diameter of the interior 211 of the pipe 210 decreases from the first value to a second value. In a third axial section 233 subsequent to the second section 232 the diameter of the interior of the pipe has the second value. Further, this third section 233 axially extends to the axial end 211 of the pipe 210.

The shroud element 220 circumferentially surrounds at least the second section 232 and the third section 233. Further, the openings 213 in the wall of the pipe 210 connecting the interior 212 of the pipe 210 and the cavities are provided in the second section 232.

As can further be seen in FIG. 2b , the cavities 221 inside the shroud element 210 can have different individual shapes. For example the above cavity 221 shown in FIG. 2b comprises three different axial sections, wherein in a first axial section adjacent to the opening 213 a radial expansion increases along the axial direction. In a second axial section subsequent to this first axial section the radial expansion decreases along the axial direction. In a third axial section subsequent to this second axial section the radial expansion increases again. The lower cavity 221 shown in FIG. 2b comprises e.g. two different axial sections, wherein in a first axial section adjacent to the opening 213 the radial expansion increases. In a second axial section subsequent to this first axial section the radial expansion decreases.

By means of the second low velocity jet 131 of oxidant surrounding the first high velocity jet 130, accretions or depositions on or near or around the tip of the fluid injection element 200 can be prevented or at least significantly reduced. The second oxidant jet 131 is particularly sucked into the first oxidant jet 130 at a position relatively close to the axial ends 211, 223 of the pipe 210 and the shroud element 220. Therefore, in this zone, in which the second oxidant jet 131 is sucked into the first oxidant jet 130, dust or dirt particles are not sucked into the first oxidant jet 130. These particles are indicated in FIG. 2b by reference numeral 240. The recirculation zone, in which these kinds of particles 240 are recirculated, is therefore moved further inside the furnace 100 away from the axial ends 211, 223 of the pipe 210 and the shroud element 220. Thus, these particles 240 cannot deposit on or near or around the tip of the fluid injection element 200. Thus, maintenance intervals of the fluid injection element 200 and therefore of the corresponding furnace 100 can be increased. Costs and effort to operate the furnace 100 can thus be reduced.

REFERENCE LIST

-   100 melting furnace, rotary furnace -   101 chamber -   102 door -   103 metallic material -   105 burner -   110 fuel injection element -   111 fuel supply -   120 oxidant injection element, fluid injection element -   121 oxidant supply -   130 first jet of oxidant -   131 second jets of oxidant -   140 control unit -   200 fluid injection element -   210 pipe -   211 axial end of the pipe 210 -   212 interior of the pipe 210 -   213 wall of the pipe 210 -   220 shroud element -   221 cavity in the shroud element 220 -   222 opening 222 of the shroud element 220 -   223 axial end of the shroud element 220 -   224 bleed hole -   225 oxidant ejected for reasons of pressure compensation -   231 first axial section -   232 second axial section -   233 third axial section -   240 particles into a vortex created by a burner 

What we claim is:
 1. A fluid injection element comprising a pipe and a shroud element, wherein the shroud element circumferentially surrounds an axial section of the pipe extending from an axial end of the pipe, characterised in that at least one cavity is provided at the shroud element, wherein the at least one cavity is in fluid communication with an interior of the pipe and wherein the at least one cavity extends to an opening at an axial end of the shroud element.
 2. The fluid injection element according to claim 1, wherein an opening in a wall of the pipe connects the interior of the pipe and the at least one cavity thereby establishing the fluid communication between the interior of the pipe and the at least one cavity.
 3. The fluid injection element according to claim 1, wherein in a first axial section of the pipe the diameter of the interior of the pipe has a first value, wherein in a second axial section of the pipe subsequent to the first axial section the diameter of the interior of the pipe decreases from the first value to a second value, wherein in a third axial section of the pipe subsequent to the second axial section the diameter of the interior of the pipe has the second value, the third axial section axially extending to the axial end of the pipe, and wherein the shroud element circumferentially surrounds at least the second axial section and the third axial section.
 4. The fluid injection element according to claim 2, wherein the opening in the wall of the pipe connecting the interior of the pipe and the at least one cavity is provided in the second section.
 5. The fluid injection element according to claim 1, wherein one single cavity continuously extends in a circumferential direction inside the shroud element or wherein several cavities are provided inside the shroud element distributed in predetermined circumferential distances to each other.
 6. The fluid injection element according to claim 1, wherein at least one bleed hole is provided in the shroud element extending from the at least one cavity to a radial end of the shroud element.
 7. The fluid injection element according to claim 1, wherein an expansion of the at least one cavity in radial direction has different values or differently varying values in different subsequent axial sections of the at least one cavity.
 8. The fluid injection element according to claim 1, wherein the pipe is adapted to be connected with a fluid supply such that a first amount of a fluid is conducted through the interior of the pipe and ejected throughout the axial end of the pipe with a first velocity, particularly a sonic or supersonic velocity, a second amount of the fluid is conducted through the at least one cavity of the shroud element and ejected throughout the opening of the at least one cavity at the axial end of the shroud element with a second velocity smaller than the first velocity.
 9. A furnace comprising a burner with a fuel supply and an oxidant supply, characterised in that at least one fluid injection element comprising a pipe and a shroud element, wherein the shroud element circumferentially surrounds an axial section of the pipe extending from an axial end of the pipe, comprising at least one cavity is provided at the shroud element, wherein the at least one cavity is in fluid communication with an interior of the pipe and wherein the at least one cavity extends to an opening at an axial end of the shroud element is provided for providing an oxidant to the burner.
 10. A method for operating a furnace, wherein fuel is provided to a burner of the furnace, wherein an oxidant is provided to the burner via at least one fluid injection element comprising a pipe and a shroud element, wherein the shroud element circumferentially surrounds an axial section of the pipe extending from an axial end of the pipe, comprising at least one cavity is provided at the shroud element, wherein the at least one cavity is in fluid communication with an interior of the pipe and wherein the at least one cavity extends to an opening at an axial end of the shroud element such that a first amount of the oxidant is provided with a first velocity, and a second amount of the oxidant is provided with a second velocity smaller than the first velocity.
 11. The method according to claim 10, wherein the first amount of the oxidant is provided as a first oxidant jet and wherein the second amount of the oxidant is provided as at least one second oxidant jet circumferentially surrounding the first oxidant jet.
 12. The method according to claim 10, wherein the first amount of the oxidant is provided via the interior of the pipe of the at least one fluid injection element and wherein the second amount of the oxidant is provided via the at least one cavity of the shroud element of the at least one fluid injection element.
 13. The method according to claim 10, wherein the first amount of the oxidant is between 75% to 90% and wherein the second amount of the oxidant is between 10% and 25%. 